.SCR FILES:
    -----------

    .SCR files are memory dumps of the first 6912 bytes of the Spectrum
    memory.  A coordinate (x,y), x between 0 and 255 and y between 0 and
    192, (0,0) being the upper left corner of the screen, corresponds to
    the pixel address

        16384+INT (x/8)+1792*INT (y/64)-2016*INT (y/8)+256*y

    I admit this is not quite the clearest way to explain the organization
    of Spectrum's video memory, but with a bit or (hard) thinking you can
    extract from above formula all information you need...  The lowest
    three bits of x determine which bit of this address corresponds to the
    pixel (x,y).  This bit-map constitutes the larger part of the screen
    memory, 256*192/8=6144 bytes.  The final 768 bytes are attribute bytes.
    The address of the attribute byte corresponding to pixel (x,y) is

        22528+INT (x/8)+32*INT (y/8)

    The lowest three bits of the attribute byte control the foreground
    color (the color of the pixel if the corresponding bit in the bitmap is
    set), bits 3-5 control the background color, bit 6 is the bright bit
    and bit 7 is the flash bit - if it is set, every 16/50th of a second
    the ULA effectively flips the foreground and background colours.